The present invention relates to a power steering device provided with a fluid pressure cylinder of the single rod type, and more particularly to a control valve for controlling changeover of a flow path in such a device.
As a fluid pressure cylinder for generating auxiliary steering power by supplying fluid pressure, a dual rod type cylinder has been most frequently used. However, a single rod type cylinder is also known which is advantageous in view of its simplified structure as well as its cost. If such a single rod type cylinder is arranged to merely selectively supply fluid pressure to either one of the chambers of the cylinder, the movement of the cylinder on opposite sides of its neutral or outer position in the axial direction of the piston is asymmetric because the opposite side chambers of the cylinder have different fluid pressure receiving areas. Hence, the magnitude of the supplied steering power for a given amount of movement of the steering wheel is different in two opposite directions, resulting in a difficulty in steering the vehicle.
Various arrangements have been proposed to solve such an asymmetric movement of piston. As disclosed in Japanese Laid-open Patent Application No. 128270/1981, a control valve for changing the characteristic of the supply flow to the rod-side chamber and the head-side chamber is provided with which the quantity of supply to the head-side chamber is decreased in accordance with the ratio of the pressure receiving area to make the respective movements of the piston in the right and left directions substantially equal. In this device, however, the structure of the control valve is necessarily complex and costly. Also, the value can be affected by the steering speed, temperature, or the like such that the same output characteristics in the right and left directions are not always obtainable.